This invention relates generally to evaporative coolers and more specifically to an electronic controller for such evaporative coolers. Evaporative coolers, also known as swamp coolers, are best suited to dry desert climates such as that found in the southwestern United States. Evaporative coolers generally comprise a generally cubical metal structure of three to four feet in length, height, and width that is mounted on the exterior of the roof of a building to be cooled. Four surfaces of the evaporative cooler comprise removabLe frames that contain pads made of shredded aspen wood or paper. The bottom of the evaporative cooler contains water to a depth that is controlled by a float to be about four inches. The water is circulated by a water pump through distribution tubes to the tops of the pads to keep them wet. A blower fan centrally located within the evaporative cooler pulls dry outside air through the wet pads and into a duct distribution system located within the building. Exemplary of such prior art evaporative coolers is that described in U.S. Pat. No. 4,379,712.
Evaporative coolers differ significantly from refrigeration or air conditioning units in a number of ways. Air conditioners employ a compressor and typically cost $200-$300 per month to operate on a demand basis, while an evaporative cooler typically costs only $35-$55 per month to operate on a 24-hour basis. An air conditioner simply recirculates the air inside the building, while an evaporative cooler permits fresh outside air, cooled through the wet pads of the evaporative cooler, to enter the building and exit through open windows. As a result, evaporative coolers deliver roughly three times the airflow volume delivered by air conditioners. In addition, air conditioners are cycled on and off during the course of the day and night by the thermostats that control them, whereas prior art evaporative coolers run continuously. Since the heat entering an air conditioned building must be removed by running the air conditioner compressor, no significant saving can be realized by turning an air conditioner off during part of the day, since it will simply run longer when turned on in order to remove the heat gained. In buildings cooled by an evaporative cooler, the heat gain is removed through open doors and windows.
One of the problems associated with prior art evaporative coolers is their high water usage on the order of 15-20 gallons per hour. Shutting the evaporative cooler off during the late night and early morning hours when it is not needed or at times when the building is not occupied can result in significant savings of water and electrical energy. For example, it has been estimated that approximately 10 billion gallons of water are used annually in Tucson, Arizona, in connection with the operation of residential evaporative coolers. This represents a significant portion of the total annual residential water usage of roughly 60 billion gallons for the entire state of Arizona.
Prior art evaporative coolers of the type commercially available are controlled by a simple rotary six-position manually operated switch that allows the user to select a combination of water pump and blower fan settings. These manual switches do not address the problem of high water usage of approximately 15-20 gallons per hour associated with the typical residential evaporative cooler. In the desert, water is precious, and the ability to control the operation of evaporative coolers would result in a significant saving of this Precious natural resource, as indicated by the example above. There have been a number of attempts in the prior art to solve the problem of controlling evaporative coolers through the use of thermostats. Exemplary of this prior art are U.S. Pat. Nos. 4,232,531, 4,560,972, 4,580,403, 4,673,028, and 4,775,100. However, control of evaporative coolers is not effectively accomplished using temperature responsive devices, for a number of reasons. In order for an evaporative cooler to work properly, some windows in the building must be open in order to relieve the air pressure created by the evaporative cooler. The open windows permit hot outside air to enter the building when the evaporative cooler is turned off by the thermostat, thereby causing rapid cycling of the evaporative cooler and defeating the purpose of the thermostat. Evaporative coolers do not recirculate and thereby mix the inside air. As a result, it is very difficult to position a thermostat for controlling an evaporative cooler in a location that will provide good temperature sensing. U.S. Pat. No. 4,560,972 describes a line voltage thermostat for controlling evaporative coolers. This device is intended to replace the conventional manually operated control switch. However, these manual switches are generally located in hallways or closets, which are unacceptable locations at which to sense the inside air temperature. In addition, thermostat control results in cooling the building, whether or not is occupied, thereby causing a waste of water and energy. The line voltage thermostats described in U.S. Pat. Nos. 4,775,100 and 4,569,972 have a wide range of plus or minus 20 degrees Fahrenheit in order to prevent rapid cycling of the evaporative cooler that would otherwise result from hot air entering the building through open windows. The use of these thermostats results in unpredictable cycling, and generally would result in the evaporative cooler being turned on and off once every day.
A problem associated with conventional manually operated evaporative cooler control switches is the fact that the blower fan motor and water pump stop and start each time the control switch is moved from one position to another. This stopping and starting causes undesirable wear of the blower fan motor and water pump. It is therefore an object of the present invention to provide a controller for evaporative coolers in which a time delay is imposed following each selection of a evaporative cooler function to inhibit starting of the blower fan motor and water pump. Another problem associated with prior art evaporative cooler controllers is the entrance of hot air into the building during start-up of the evaporative cooler, since approximately five minutes are required from the time the evaporative cooler is started until the pads become wet. During this time, the evaporative cooler blows hot air and creates an uncomfortable temperature environment within the building. It is therefore an object of the present invention to provide a controller for evaporative coolers having a pre-wet feature that causes engagement of the water pump for a period of time sufficient to wet the evaporative cooler pads before the blower fan motor is engaged. Yet another problem associated with prior art evaporative cooler controllers is the lack of electrical system diagnostics. It is therefore an object of the present invention to provide a controller for evaporative coolers having visual indicators for use in diagnosing faults in various components of the controller. U.S. Pat. Nos. 4,673,028 and 4,580,403 describe evaporative cooler controllers that require additional electrical wiring and constructional changes to buildings in which an evaporative cooler has been previously installed. It is therefore an object of the present invention to provide a controller for evaporative coolers that is adapted to directly replace a previously installed conventional manually operated control switch without the need for electrical wiring or structural changes.